The invention concerns a drive system for utility vehicles, in particular for agricultural or industrial tractors, with a generator driven by an internal combustion engine, with at least one drive axle, each of whose wheels is driven by an associated electric motor supplied by the generator, with at least one steering axle whose wheels are steered in common or individually by steering actuators, and with manual operating devices for at least the drive functions of steering and the speed input.
Utility vehicles and, in particular, agricultural tractors are driven at present by internal combustion engines and a multiplicity of gearbox types that differ in design and number of gear ratios. Drive systems are also known from U.S. Pat. No. 4,953,646, issued Sep. 4, 1990 to Kim, in which the internal combustion engine drives a generator which supplies current to two single wheel electric motors of a vehicle drive axle. In place of such a pure electric drive, U.S. Pat. No. 5,947,855, issued Jul. 9, 1999 and assigned to the assignee of this application, proposed a vehicle with a torque division electromechanical single wheel drive, in which the present invention can fundamentally be applied as well.
To supply the drive functions manual operating devices are applied that transmit the high priority steering wheel and brake pedal operations directly by mechanical and/or hydraulic means, that is, between the steering wheel and the steering arrangement as well as between the brake pedal and the brakes there exists a mechanical or hydro-mechanical connection. Up to the present time this has been required by law fundamentally for all utility vehicles for safety reasons. For agricultural tractors, which are permitted to operate only at speeds up to 40 Km/h, an exception permits the operation of the high priority steering arrangements and brakes by hydraulic servo systems. As a rule a number of low priority operating functions (for example, the speed input) are also preset directly. However, U.S. Pat. No. 5,575,737, issued Nov. 19, 1996 and assigned to the assignee of this application, also proposed the indirect input of lower priority operating functions electronically, in particular by means of a user interface.
By making additional functions available through which the maneuverability of the vehicle during operation or the steering capacity and safety during over-the-road operation are to be improved, the drive concept of the utility vehicle becomes ever more complex.
The goal of the invention is to reconsider the operation of all operating functions and to organize them uniformly anew as far as possible. Here it is desirable, in vehicles with a generator and electric single-wheel motors in which, for example, all four quadrants of the drive system are utilized for forward and reverse operation as well as for braking, to process together the functions of steering, driving and, if necessary also, of braking.
It also appears possible to shift the function of speed control to the electric single-wheel drives. Then the transmission as a mechanical unit as well as the axle functions with axle differential, differential lock etc. as well as the possible central differential with the central differential lock and even the braking function in retarder operation can be omitted or at least carry a reduced load. Thereby a multitude of costly components could be omitted and the operating functions could be arranged uniformly. The inclusion of further vehicle functions into the drive control is highly desirable. For the inclusion of high priority steering wheel and brake pedal actuation, however, high safety requirements must be met, which at present stand in the way of such an inclusion.